This section specifies the semantics of statements in Cx.

Assert

Asserts that an expression is true. Useful for verification.

Assignment

Assign an expression to a variable or an array.

x = 15;
y[3] = (u4) z;

The assignment statement may be used without a target variable just to force the evaluation of an expression. This is useful to wait for an event by reading from a sync port, but without using the actual data. In this case, you can use an empty assignment statement as follows:

in sync u8 msg;
void loop() {
  // ...
  // wait for data to be available on msg, and discard it
  msg.read();
  // ...
}

Fence

Placed between statements, forces a new cycle to start.

print("in cycle 1");
fence;
print("in cycle 2");

Idle

Do nothing for a given number of cycles.

print("in cycle 1");
idle(3);
print("in cycle 5");

Print

Prints a message/values. Useful for verification.

print("something");

Return

Returns a value. In the current version, only valid at the end of a constant function.

return factor << 1;

Write

Write to a port.

answer.write(42);

If

Conditional "if" statement.

if (a > 0) {
  print("a greater than zero");
} else if (a < 0) {
  print("a smaller than zero");
} else {
  print("a equals zero");
}

Both if and for statements have special semantics of reads in conditional called peeking. This means that you may read the data on a port in the condition of the if/loop and still have access to that data in the branch that is chosen:

if (a.read() < b.read()) { // peeks a and b
  min.write(a.read()); // does not cause a new cycle,
}
// we're still in the same cycle
// after the if, both a and b have been read (b implicitly in this case)

b.read(); // causes the creation of a new cycle

For

For loop with initial assignment, loop condition, post-iteration assignment.

for (u4 i = 0; i < 5; i++) {
  print("one iteration"); // this message is printed 5 times in the current cycle
}

for (; cond.read(); count++) {
  print("cond is true"); // this message is printed one time per cycle until cond becomes false
}

A for loop can be executed in the current cycle if the following conditions are respected:

  • The loop uses a local variable used solely for iteration.
  • The loop has compile-time constant bounds.
  • The body does not read or write ports, or contains fence or idle instructions.

Otherwise, the loop takes at least one cycle per iteration.

While

While loop with loop condition.

while (keepGoing.read()) {
  count++;
}

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